The present invention relates to a method of manufacturing a crown-shaped component for a torque sensor. Particularly, the present invention relates to a method of manufacturing a crown-shaped component which has a plurality of axially extending protrusions that are formed at an end of a cylindrical portion thereof, by using forging, annealing, cutting, shot blasting and the like.
Conventionally, a torque sensor, which-is attached to an electric power steering of a motor vehicle so as to detect a steering torque, is constructed as follows. An crown-shaped component 3 is set at a joint portion between the input and output components of a steering shaft, and a detecting coil is applied around them. The crown-shaped component 3 has a complicated shape, as shown in FIG. 1. The crown-shaped component 3 has a plurality of axially extending protrusions 2 which are formed at an end of a cylindrical portion 1 thereof.
In one of conventional manufacturing methods, the crown-shaped component 3 is manufactured by a powder sintering method in which powder of magnetic stainless steel is pressure-molded and sintered. In the other of conventional manufacturing methods for manufacturing the crown-shaped component, forging and cutting are utilized as disclosed in a Japanese Patent Unexamined Publication No. Hei.8-240493.
The conventional powder sintering method is disadvantageous in that since the product undergoes the complicated manufacturing process, the cost to manufacture is increased, and since perforations are easily formed in the product, a rigidity of the product becomes insufficient.
The conventional forging and cutting process also has disadvantages. The crown-shaped component, which is manufactured by the conventional forging and cutting process, inevitably suffers from the residual distortion and formation of burrs. Accordingly, a variation of the magnetic characteristic is great, and a high detection accuracy is not secured. This is a problem, because magnetic characteristic of the crown-shaped component greatly affects the sensing ability of the magnetic sensor.
Accordingly, an object of the present invention is to provide a method of manufacturing a crown-shaped component for a torque sensor, wherein the crown-shaped component has a stable magnetic characteristic. In addition to this, it is also an object of the present invention to provide a manufacturing method of such crown-shaped component with low cost.
The mentioned object can be achieved by, according to the present invention, a method of manufacturing a crown-shaped component having a plurality of axially extending protrusions which are formed at an end of a cylindrical portion thereof. The manufacturing method comprises the steps of:
upsetting and forming a cylindrical-shaped blank into a cylindrical-shaped member that includes a cylindrical portion, a plurality of protrusions formed at the top end of the cylindrical portion, an annular-shaped remaining part connected to the cylindrical portion, said protrusions being arrayed on and along the inner circumferential surface of the remaining;
annealing the thus upset and formed cylindrical-shaped member;
cutting and removing the remaining part from the thus annealed cylindrical-shaped member so as to form a crown-shaped member which is substantially coincided with the crown-shaped component in shape;
shot-blasting the crown-shaped member.
In the manufacturing method according to the present invention, it is preferable that the shot-blasting step comprises the step of:
dry shot blasting the crown-shaped member.
Further, in the above-mentioned manufacturing method according to the present invention, it is more preferable that the blowing pressure of the dry shot blasting is set to be in the range from 3 to 5 kgf/cm2, and the blooming time thereof is set to be in the range of 10 to 30 seconds.
Moreover, the manufacturing method according to the present invention, it is advantageous that the upsetting and deforming step comprising the steps of:
upsetting the cylindrical-shaped blank into a first cylindrical-shaped member that includes a cylindrical basal portion, the protrusions protruding from the cylindrical basal portion in an axial direction thereof, and the remaining part that extends in a circumferential direction thereof and is connected to the cylindrical basal portion;
deep-drawing the thus upset first cylindrical-shaped member into a second cylindrical-shaped member that includes the plurality of protrusions, the remaining part and a cylindrical basal portion that has a bottom part and a C-shaped cross-section;
punching and removing the bottom part of the thus deep-drawn second cylindrical-shaped member so as to form a third cylindrical-shaped member that includes the plurality of protrusions, the remaining part and a cylindrical basal hollow-portion as the cylindrical portion.